An automotive window regulator generally comprises the combination of a relatively small electric motor which is connected through a reduction drive, a drum and two or more cables to at least one slide/carrier plate assembly to which the window glass is attached when assembled into an automobile door or hatch. When the motor is operated it winds and unwinds the cables so as to cause the carrier plate or plates to travel along the slide or slides. When a window is attached to the carrier plate or plates, it moves in the open or close directions according to the direction of motor travel.
Manufacturing defects occasionally make such window regulators unacceptably noisy such that operation thereof in an automobile is displeasing to the owner. Noise can be the result of a number of different factors including motor armature imbalance, defective motor bearings, irregular motor commutator surfaces causing brush bounce or rattle, and surface imperfections such as dents and burrs in the finish of the metal slide where it is contacted by the carrier plate.
Noise produced by an installed window regulator tends to be amplified by the automobile door panels and, therefore, a regulator which may not sound particularly noisy before installation may be unacceptably noisy after installation. There is a significant advantage in identifying unacceptably noisy window regulators prior to installation into the automobile since replacement of the regulator after installation is more costly than discarding a faulty regulator prior to assembly into an automobile.
To our knowledge, window regulators have not been routinely tested for noise on the factory floor during the assembly process. We believe that this is due to the fact that ambient noise levels are too high in most factories to use microphonic pickups for noise detection. While this problem could be solved by removing the regulator to a noise-insulated test chamber, it is impractical to do this with every regulator made in a mass-production facility.